Roads,airfield runways and the like

ABSTRACT

A METHOD OF PRODUCING AN ARTIFICIAL ROADSTONE SUTITABLE FOR USE IN A BITMUINOUS SURFACING COMPOSITION FOR ROADS, ARIFIELD RUNWAYS AND THE LIKE. THE METHOD COMPRISES THE STEPS OF (A) FORMING A MIXTURE OF A GRANULAR AGGREGATE A SOLID BONDING MATERIAL, AND WATER, THE GRANULAR AGGREGATE AND BONDING MTERIAL BEING PRESENT IN SPECIFIED PROPORTIONS AND SIZE AND HAVING SPECIFIED COMPOSITIONS, (B) COMPACTING THE MIXTURE UNDER A PRESSURE OF AT LEAST 1/2 LONG TON PER SQUARE INCH TO FORM A COHERENT BODY, (C) HARDENING THE COHERENT BODY, AND (D) CRUSHING THE HARDENED COHERENT BODY TO FORM THE DESIRED ARTIFICIAL ROADSTONE,

M 16, 1914 D. M. RICHARDS 3,324,109

ROADS, AIRFIELD RUNWAYS AND THE LIKE I 2 Sheets-Sheet '1 Original Filed March 21, 1969 u, NLRICHARDS ROADS, AIRFIELD RUNWAYS AND THE LIKE 2 Sheets-Sheet United States Patent O 3,824,109 ROADS, AIRFIELD RUNWAYS AND THE LIKE Dennis Maunder Richards, St. Austell, Cornwall, England, assignor to English Clays Levering Pochin & Company Limited, St. Austell, Cornwall, England Continuation of abandoned application Ser. No. 809,126, Mar. 21, 1969. This application June 20, 1972, Ser. No. 264,421

Int. Cl. C08h 13/00, 17/02; C09d 3/24 U.S. Cl. 106-281 R 13 Claims ABSTRACT OF THE DISCLOSURE A method of producing an artificial roadstone suitable for use in a bituminous surfacing composition for roads, airfield runways and the like. The method comprises the steps of (a) forming a mixture of a granular aggregate, a solid bonding material, and water, the granular aggregate and bonding material being present in specified proportions and sizes and having specified compositions, (b) compacting the mixture under a pressure of at least /2 long ton per square inch to form a coherent body, (c) hardening the coherent body, and (d) crushing the hardened coherent body to form the desired artificial roadstone.

This is a continuation of application Ser. No. 809,126, filed Mar. 21, 1969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to roads, airfield runways and the like and, more particularly but not exclusively, is concerned with an artificial roadstone suitable for use in bituminous surfacing compositions.

A bituminous surfacing composition is a mixture of aggregates and a hinder, the binder essentially comprising a bituminous material. By the term bituminous ma terial there is meant herein a viscous, semi-solid material which can be easily melted and which has marked agglomerating properties at atmospheric temperatures. Conventional aggregates can be classified into eleven main groups viz. (l) artificial, e.g. slags, clinker etc., (2) basalt, (3) flint, (4) gabbro, (5) granite, (6) gritstone, (7) hornfels, (8) limestone, (9) porphyry, (10) quartzite and (11) schist. Bituminous surfacing compositions comprise two main categories, namely asphalt, in which the binder comprises bitumen, and tarmacadam, in which the binder comprises tar. For roads carrying moderate to heavy traific, i.e. more than about 450 commercial vehicles per day, it is usual practice to construct the surface of the road in two layers i.e. a base course of thickness 1% to 2% inches and a top, wearing course of thick ness to 1 /2 inch, the wearing course containing an aggregate consisting of pieces of smaller mean size than that used in the base course. One type of wearing course which is frequently used is known as rolled asphalt and is produced from a bituminous surfacing composition comprising aggregate and relatively hard bitumen, the composition being heated to a temperature at which it can be spread by rakes or a mechanical spreader and then compacted with a roller. The bituminous surfacing compositions generally used for rolled asphalt wearing courses for heavy traffic have the following range of compositions:

(A) Coarse aggregate: O to 55% by weight (B) Fine aggregate: 20 to 80% by Weight (C) Filler: 4 to 18% by weight (D) Bitumen: 5 to 13% by Weight.

The coarse aggregate (A) comprises pieces which are retained on a No. 7 mesh British Standard sieve and which 3,824,109 Patented July 16, 1974 ice are classified to give as nearly as possible pieces of uniform size and shape. The side of the pieces should be not more than /2 and not less than Vs the thickness of the wearing course and should lie broadly in the range A to 4 inch. The materials most commonly used as coarse aggregate include broken stone, mineral ore, slag and gravel. The fine aggregate (B) comprises particles having a size distribution such that substantially all the material passes a No. 7 mesh British Standard sieve and is retained on a No. 200* mesh British Standard sieve. The materials most commonly used for fine aggregate include natural sand or crushed rock. The filler (C), which is required to stiffen and strengthen the bitumen and fill up the voids in the composition to render the surface impervious to water, comprises material all of which passes a No. 200 mesh British Standard sieve. Practically any inert mineral powder of the required fineness is suitable for use as a filler, but limestone dust is most commonly used although Portland cement and slate dust are also frequently used.

The properties of an aggregate which are of most importance in road making are its resistance to crushing, impact, abrasion and polishing, its specific gravity and water absorption, and its grading and particle shape. If an aggregate is to be used in the Wearing course of a road or the like carrying heavy trafiic, the resistance of the aggregate to crushing, abrasion and polishing are of particular importance. Tests for measuring the resistance of an aggregate to crushing, abrasion and polishing are described in British Standard 812:1967, pages 71-97, and the results of these tests are recorded as the aggregate crushing value, the aggregate impact value, the 10 percent fines value, the aggregate abrasion 'value and the polished stone value." The aggregate crushing value varies for conventional aggregates from about 10% for some hornfels to about 30% for some limestones; the aggregate impact value varies for conventional aggregates from about 7% to about 25%; the 10 percent fines value varies for conventional aggregates from about 40 tons for the strongest aggregates down to as little as 1 ton for material such as chalk; the aggregate abrasion value varies from below 1% for some flints to over 20% for aggregates that would normally be regarded as too soft for use in the wearing course of a road surface; and the polished stone value varies from about 27 for certain limestones to about 74 for certain members of the gritstone class. For the wearing course of a road or the like carrying heavy traflic it is important to use as the aggregate, particularly the coarse aggregate, of a bituminous surfacing composition material having a high polished stone value i.e. greater than '62, and a high resistance to crushing and abrasion i.e. a maximum aggregate impact value of 30%, a maximum aggregate crushing value of 30% and a maximum aggregate abrasion value of 20%; but natural stones having these properties are in short supply and, as a consequence, expensive.

It is an object of the present invention to provide a method of producing artificial roadstone which is suitable for use as an aggregate in a bituminous surfacing composition for a wearing course of a road, airfield runway or the like, having a high polished stone value as well as a high resistance to crushing and abrasion.

SUMMARY OF THE INVENTION According to one aspect of the present invention, therefore, there is provided a method of producing an artificial roadstone which method comprises the steps of (a) forming a mixture of a granular aggregate, a bonding material and water, wherein the granular aggregate constitutes from 40% to by weight of the solids in said mixture and is composed wholly or substantially wholly of siliceous material passing a inch mesh British Standard sieve and retained on a No. 100 mesh British Standard sieve, wherein the bonding material constitutes from to 60% by weight of the solids in said mixture and has a particle size distribution such that substantially all thereof passes a No. 100 mesh British Standard sieve and a composition such that at least 50% by weight thereof is composed of materials capable of forming on reaction with water stable, substantially insoluble hydrated calcium silicates and/or calcium aluminates, and wherein the quantity of water in the mixture is in the range of from 3% to 10% by weight, based on the total weight of solids in said mixture, (b) compacting the mixture under a pressure of at least /2 long ton per square inch, to form a coherent body, (c) hardening the coherent body, and (d) crushing the hardened coherent body to form the desired artificial roadstone.

in another aspect, the present invention provides a bituminous surfacing composition which comprises a mixture of an aggregate and a bituminous material, the aggregate comprising artificial roadstones produced by the method of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferably, the granular aggregate constitutes less than 80% by weight of the solids in the mixture and the bonding material constitutes more than by weight of the solids in said mixture. The granular aggregate used in forming the artificial roadstone of the present invention consists wholly or substantially Wholly of siliceous material passing a inch British Standard sieve and retained on a No. 100 mesh British Standard sieve and can be, for example, a naturally fine or artificially ground sand or siliceous rock or quarry material. Advantageously the granular aggregate will comprise at least 20% by weight of material passing a No. mesh British Standard sieve.

The bonding material used in forming the artificial roadstone of the present invention preferably comprises a mixture of finely divided siliceous material, e.g. silica flour and/or slate powder (which generally contains from 50 to 70% by Weight of free silica), and lime which can be in the form of hydrated lime, quick lime or spent calcium carbide or a mixture of two or more thereof. The bonding material can also include a Portland cement or a high alumina cement. The bonding material advantageously has a composition such that the molar ratio of CaOsSiO is in the range 1:1.5 to 1:25 and most advantageously is about 1:2.0. When the bonding material contains materials other than those capable of forming hydrated calcium silicates and/or calcium aluminates such other materials should be substantially inert. Moreover, as the amount of the inert material present in the bonding material is increased so the amount of bonding material in the mixture of aggregate and bonding material is increased.

The water content of the mixture should be in the range of from 3% to 10% by weight, and preferably is in the range 4% to 8% by weight, based on the total weight of solids in the mixture.

The mixture of granular aggregate, bonding material and water is compacted and then hardened, generally but not necessarily by treatment with steam, preferably under conditions of elevated pressure, for example in an autoclave. The process of compacting the mixture of granular aggregate, bonding material and water can be performed, for example, in a conventional brick press. The pressure used during the compacting is at least /2 long ton per square inch and preferably is in the range of from 2 to 4 long tons per square inch. Compacting pressures nearer the lower limit will be used when the water content of the mixture is nearer the upper limit. After compacting, the coherent, or green product, thus formed, is hardened. Unless the bonding material contains a significant proportion of a high alumina cement the hardening is effected by treatment with steam which is preferably under a pressure of at least p.s.i.g., most preferably under a pressure in the range of from 220 to 240 p.s.i.g. The steam treatment is carried out for at least one hour, the higher steam pressures requiring shorter times. At the preferred steam pressures of 220 to 240 p.s.i.g. the time required is in the range 3 to 5 hours.

The hardened coherent body can be crushed to form the desired artificial roadstone in one or two stages.

In a single stage process, the coherent body is fed to a crusher, which can be, for example, a jaw crusher, a gyratory crusher, a single roll crusher or a hammer mill, and the crushed material passed through a series of screens to classify the material into desired size ranges. For example, the first screen could correspond to the maximum permissible size, generally inch, for roadstone to be used in a coarse aggregate, the material retained on this first screen being returned to the crusher. The crushed material passing the first screen, i.e. material less than inch in size, may be graded into a series of single sizes, e.g. A1 inch to A: inch, /2 inch to /8 inch, and inch to inch, by means of screens of appropriate aperture size. These single sizes may be recombined in any proportion to give a coarse aggregate consisting of pieces having a size distribution specified for a particular use. Thus, the final screen in the series may have, for example, apertures of -a size equivalent to a No. 7 mesh British Standard sieve and material passing this final screen can be used as a fine aggregate, after the removal therefrom of material passing a :No. 200 mesh British Standard sieve, or can be used as granular aggregate in the method of producing the hardened coherent body.

Although the hardened coherent body can be crushed in a single stage, it is found to be preferable to perform the crushing in two stages because, in order to obtain an artificial roadstone of substantially uniform size and shape; the reduction ratio, i.e. the ratio of the size of the aperture passing all the feed to the crusher to the size of the aperture passing all the product of the crusher, should not be greater than 4:1. In a two-stage crushing process the primary crusher can be one of the types of crusher noted above and the secondary crusher can be, for example, a reduction gyratory crusher, a cone crusher or a hammer mill. A screen having an aperture size in the range 2 to 3 inches is provided between the primary and secondary crushers and material retained on this first screen is fed back to the primary crusher. Material pass ing the first screen but retained on a second screen having an aperture size of inch is fed to the secondary crusher and returned to the second screen after further crushing. Material passing the second screen can be classified in the same way as described above in connection with the single stage process.

For a better understanding of the method of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which FIGS. 1 and 2 are schematic diagrams of two installations suitable for carrying out the method of the invention.

Referring first to FIG. 1, it will be seen that granular aggregate, lime and silica flour are stored in three storage bins 1, 2 and 3, respectively. Further storage bins can be provided for storing other materials, e.g. Portland cement. Material from these storage bins, together with water W, is fed to a mixer 4 in the appropriate proportions. After mixing, the mixture of granular aggregate, lime and silica flour is introduced into a brick press 5 and is compacted therein to form a coherent compacted body. The coherent compacted body is then transferred to an autoclave 6 in which is it treated with steam S. After completion of the steam treatment, the hardened coherent body is allowed to cool and is then fed to a jaw crusher 7. The crushed material is passed through a series of screens 8 to 12 having aperture sizes of /1 inch, /2 inch, inch, inch and No. 7 mesh British Standard sieve, respectively, which classify the crushed material into various size ranges. The material retained on the first screen 8 is returned for further crushing to the jaw crusher 7. The material passing the final screen 12 is either further classified on a screen 13, in order to separate therefrom material passing a No. 200 mesh British Standard sieve, and used as fine aggregate or is returned to the storage bin 1 for use as aggregate in the method of the present invention.

FIG. 2 of the accompanying drawing shows schematically an installation similar to that described with reference to FIG. 1 but in which the cooled, hardened coherent body from the autoclave is crushed in two stages. In this method the material from the jaw crusher 7 is fed to a screen 14 having an aperture size of 2 inches and the material retained on this screen is returned to the jaw crusher 7 for further crushing. Material passing through the screen 14 is then passed through a series of screens 8 to 12 in a similar manner to that described above. The material retained on the screen 8 being fed to a cone crusher 15 wherein it is further crushed and then returned to screen 8. The material passing screen 12 is treated in a similar way to that described with reference to FIG. 1.

The invention is further illustrated by the following Examples. 1

EXAMPLE 1 A batch of bricks was made from the following ingredients: (1) Granular aggregate:

(a) Washed and crushed basalt having a particle size such that 100% passed a 4; inch British Standard sieve and 55% passed a No. 25 mesh British Standard sieve, 39% by weight (b) Pea gravel prepared from washed china clay waste sand and having a particle size such that 100% passed a inch British Standard sieve and passed a No. 7 mesh British Standard sieve, 31% by weight (2) Bonding material:

(a) Silica flour, by weight (b) Washed and crushed basalt comprising 50% free silica and having a particle size such that 100% passed a No. 100 mesh British Standard sieve, 7% by weight (c) Quick lime, 8% by weight The molar ratio CaO:SiO of the bonding material was 1:2.16. (3) Water (based on total dry weight of the mixture of (1) and (2)), 7% by weight.

The silica flour used as part of the bonding material had been finely ground so that 100% passed a No. 100 mesh British Standard sieve, 90% by weight passed a No. 300 mesh British Standard sieve, 25% by weight consisted of particles smaller than 10 microns and 4%;- by weight consisted of particles smaller than 2 microns.

The granular aggregate, bonding material and water were intimately mixed, and the mixture was compacted in a brick press at a pressure of 3 long tons per square inch (472 kg./cm. The coherent compacted vbodies thus formed were hardened by treatment with steam in an autoclave for 4% hours at a maximum pressure of 225 p.s.i.g. For this treatment the pressure in the autoclave was raised from atmospheric pressure to 50 p.s.i.g. in 30 minutes, and from 50 p.s.i.g. to 225 p.s.i.g. in a further 60 minutes, and this elevated pressure was maintained throughout the remainder of the processing time. After the hardening treatment had been completed, the pressure was reduced to atmospheric and the bricks were removed and allowed to cool.

The bricks, when cool, were crushed in a two stage process as described above in connection with FIG. 2 of the accompanying drawings to form artificial roadstones in accordance with the invention. The fraction of roadstones ranging in size from "V2 inch to inch was used to provide samples for measurement of the aggregate crushing value, the aggregate impact value and the aggregate abrasion value, and the fraction ranging in size from inch to ,5 inch was used to measure the polished stone value. The results of these tests were as follows:

Aggregate crushing value percent 21 Aggregate impact value -do 13.2 Aggregate abrasion value do 18.0 Polished stone value 72 The artificial roadstones manufactured above were incorporated in a flexible pavement designed to carry a trafiic flow of more than 4,500 commercial vehicles per day. The pavement was laid on a subgrade of compacted, well-drained, silty clay and consisted of an 8 inch thickness of crushed rock and sand as a sub-base, an 8 inch thickness of bitumen macadam as a base and a surface which comprised a 2 /2 inch thick base course and a 1 inch thick wearing course both consisting of rolled asphalt. The wearing course contained 25% by weight of coarse rock aggregate, 57% by weight of river-bed sand, 10% by weight of limestone filler and 8% by weight of bitumen, and into this wearing course while still warm there was rolled a coating of roadstones distributed at the rate of 130 square yard/ton (9.4 kg./m. The roadstones, which were prepared by the method of the invention, were coated with 2% by weight, based on the weight of roadstones, of bitumen having a penetration at 77 F. (25 C.) of 60. 2% by weight of a limestone filler, based on the weight of the roadstones, was also added to enable the roadstones to carry the specified proportion of bitumen.

EXAMPLE 2 A batch of bricks was made from the following ingredients:

(1) Granular aggregate:

Washed china clay waste sand having a particle size such that passed a No. 7 mesh British Standard sieve, and 78.5% passed a No. 25 mesh British Standard sieve, 41% by weight (2) Bonding material:

(a) Silica flour, 30% by weight (b)' Washed china clay waste sand having a particle size such that 100% passed a No. 100 mesh British Standard sieve, 9% by weight (c) Hydrated lime, 15% by weight (d) Portland cement, 5% by weight The molar ratio CaOzSiO of the bonding material was 1:2.08.

(3) Water (based on total dry weight of mixture of (1) and (2)), 7% by weight.

The silica flour used was the same as that used in Example 1, and the mixing, compacting, steam hardening and crushing stages were identical to those described in Example 1.

Samples of the roadstones thus prepared and having the sizes specified in Example 1 were used to measure the aggregate crushing value, the aggregate impact value, the aggregate abrasion value and the polished stone value with the following results:

Aggregate crushing value percent 22 Aggregate impact value do- 16 Aggregate abrasion value do 13 Polished stone value 78 EXAMPLE 3 A batch of bricks was made from the following ingredients:

( 1) Granular aggregate:

Washed china clay waste sand having a particle size such that 88% passed a N0. 7 mesh British Standard sieve and 29% passed a No. 25 mesh British Standard sieve, 40% by weight 7 (2) Bonding material:

(a) Silica flour, 37% by weight (b) Hydrated lime, 18% by weight Portland cement, by weight The molar ratio CaO:SiO of the bonding material was 121.71. (3) Water (based on total dry weight of mixture of (1) and (2)), 7% by weight.

The silica flour used was the same as that used in Examples 1 and 2, and the mixing, compacting, steam hardening and crushing stages were dentical to those described in Example 1.

Samples of roadstones thus prepared and having the sizes specified in Example 1 were used to measure the aggregate crushing value, the aggregate abrasion values and the polished stone value with the following results:

Aggregate crushing value percent 19 Aggregate impact value do 15 Aggregate abrasion value -do 9 Polished stone value 76 In addition to their use in bituminous surfacing compositions, the artificial roadstones produced by the method of the present invention can be used, for example, in concrete surfaces etc.

What is claimed is:

1. A method of forming a bituminous surfacing composition comprising (a) forming a mixture of a granular aggregate, an

inorganic bonding material and water wherein said granular aggregate constitutes from 40% to 90% by weight of the solids in said mixture and is composed substantially wholly of siliceous material passing a inch mesh British Standard sieve and retained on a No. 100 mesh British Standard sieve,

wherein said bonding material constitutes from 10% to 60% by weight of the solids in said mixture and has a particle size distribution such that substantially all thereof passes a No. 100 mesh British Standard sieve and comprises at least 50% by weight thereof of materials capable of forming on reaction with water at least one of stable, substantially insoluble hydrated calcium silicates and calcium aluminates, and 0 to 50% by weight thereof substantially inert material incapable of forming on reaction with water at least one of stable, substantially insoluble hydrated calcium silicates and calcium aluminates, and

wherein the quantity of water in said mixture is in the range of from 3% to 10% by weight, based upon the total weight of solids in said mixture,

(b) compacting said mixture under a pressure of at least /2 long ton per square inch to form a coherent body,

(0) hardening said coherent body,

(d) crushing said hardened coherent body and classifying the crushed body to form artificial roadstones consisting essentially of material ranging in size from about inch to about No. 7 mesh British Standard sieve and having a high polished stone value and a high resistance to crushing and abrasion, and

(e) admixing the artificial roadstones with a bituminous material.

2. A method according to claim 1, wherein the bituminous material is bitumen.

3. A method according to claim 1, wherein the bituminous material is bitumen.

4. A method according to claim 1, wherein the granular aggregate constitutes less than by weight of the solids in the mixture and the bonding material constitutes more than 20% by weight of the solids in said mixture.

5. A method according to claim 4, wherein the granular aggregate comprises at least 20% by Weight of material passing a No. 25 mesh British Standard sieve.

6. A method according to claim 1, wherein the bonding material comprises a mixture of finely divided siliceous material and lime.

7. A method according to claim 6, wherein the bonding material also includes a Portland cement.

8. A method according to claim 6, wherein the bonding material has a composition such that the molar ratio CaOzSiO is in the range 1:15 to 1:25.

9. A method according to claim 1, wherein the quantity of water in the mixture is in the range of from 4% to 8% by weight, based on the total weight of solids in the mixture.

10. A method according to claim 1, wherein the mixture is compacted under a pressure in the range of from 2 to 4 long tons per square inch to form a coherent body.

11. A method according to claim 1, wherein the coherent body is hardened by treatment with steam.

12. A method according to claim 11, wherein the coherent body is hardened by treatment with steam at a pressure in the range of from 220 to 240 p.s.i.g.

13. A method according to claim 1, wherein the hardened coherent body is crushed in two stages.

References Cited UNITED STATES PATENTS 2,758,033 8/1956 Burney, Jr. et a1. 106-97 3,078,175 2/ 1963 De Lisle 106-97 3,230,103 1/1966 Minnick 106117 3,432,322 3/1969 Rogers l06281 3,501,323 3/1970 Moorehead 106--97 JOSEPH L. SCHOFER, Primary Examiner J. B. EVANS, Assistant Examiner US. Cl. X.R.

106-283, 288 B, 308 B, 308 G, 309; 117-27, 70, 92, 

